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PREEMPTIVE_OS_GETDISKFREESPACE

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Description:

This wait type is when a thread is calling the Windows GetDiskFreeSpace function.

(Books Online description: N/A)

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Added in SQL Server version:

2008

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 453 in 2008 and 2008 R2, 501 in 2012, and 517 in 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.

Other information:

I have not seen this wait type be a noticeable contention point.

Note that when a thread calls out to Windows, the thread changes from non-preemptive (SQL Server controls the thread) to preemptive (Windows controls the thread) mode. The thread’s state will be listed as RUNNING, as SQL Server doesn’t know what Windows is doing with the thread.

Known occurrences in SQL Server (list number matches call stack list):

  1. Getting the volume free space (in this case, as part of performing a RESTORE DATABASE operation)
  2. Getting the volume free space (in this case, as part of growing the log file while adding log records)

And other similar call stacks.

Abbreviated call stacks (list number matches known occurrences list):

  1. SOS_Task::PopWait+b1
    AutoSwitchPreemptive::~AutoSwitchPreemptive+95
    StorageUnitVolume::GetSpaceAvailable+243
    BackupOperation::PlanPhysicalConfiguration+7a7
    BackupOperation::PlanFullRestore+a7
    BackupOperation::PlanRestore+be4
    BackupOperation::Restore+262
    BackupEntry::RestoreDatabase+254
    CStmtLoadDb::XretExecute+125
    CMsqlExecContext::ExecuteStmts<1,1>+427
    CMsqlExecContext::FExecute+a43
    CSQLSource::Execute+86c
    process_request+a57
    process_commands+4a3
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+ab
  2. SOS_Task::PopWait+b1
    AutoSwitchPreemptive::~AutoSwitchPreemptive+95
    FCB::NumPagesToGrowFile+2ab
    SQLServerLogMgr::GrowAFile+63e
    SQLServerLogMgr::ReserveAndAppend+292
    XdesRMReadWrite::GenerateLogRec+615
    PFSPageRef::ModifyPFSRow+5ed
    DeAllocMgr::DeAllocatePageInternal+69b
    DeAllocMgr::DropAllocUnitInternal+158b
    DropAllocationUnit+18a
    sort_clean+388
    RowsetSorted::DeleteSort+1ce
    CQScanSortNew::SortChangeState+81
    CQScanSortNew::GetRowHelper+9a
    CQScanSegmentNew::GetRow+43
    CQScanSeqProjectNew::GetRow+20
    CQScanStreamAggregateNew::GetRowHelper+1fc
    CQScanStreamAggregateNew::GetCalculatedRow+21
    CQueryScan::StartupQuery+23c
    CXStmtQuery::SetupQueryScanAndExpression+2e5
    CXStmtQuery::InitForExecute+34
    CXStmtQuery::ErsqExecuteQuery+36d